The bridge arrangement is in form of a Wheatstone bridge. When, for example, it is desired to steer a vehicle equipped with such a steering unit to the left, the first left orifice is opened and the second right orifice is opened. The other two orifices of the bridge arrangement are closed. Hydraulic fluid under pressure from the pressure port flows through the first left orifice, the left working flow path to the left working port and is supplied to a steering motor which is connected to the working port arrangement. Fluid displaced from the steering motor enters the steering unit through the right working port and flows through the right working flow path, the second right orifice and the tank flow path back to the tank port.
The use of neutral open orifices has the advantage that steering can be performed very smoothly out of the neutral position. A variable neutral open orifice allows a small predetermined flow even in the neutral position of the steering unit.